'Sweetheart' is a nice old-fashioned word that covers both. It's not used much these days, but it does answer your question.
'Partner' works, but it's mainly for adult, more 'settled' couples. It's not something teenagers would use, for example.
Some people use the expression 'my/his/her other half' to refer to a partner, but this is also for adult couples.
Or how about 'squeeze' ?? I've seen that on the celebrity pages ....